Previous studies that have examined the role of the gustatory thalamus (GT) in taste-guided behavior have not taken into account the fact that gustation involves sensory, hedonic, postingestive and, in some instances, learning processes. The proposed experiments will use rats with bilateral electrophysiologically-guided electrolytic lesions of the GT to determine how each of these processes influences taste-guided behavior. The specific aims of the proposed research are to determine if rats with GT lesions: l) experience a sensory loss; 2) fail to respond in a normal fashion to hedonically-charged gustatory stimuli; 3) are unable to utilize postingestive feedback; or 4) are unable to learn associations that involve taste cues. A lesion-induced sensory loss (Specific Aim #l) and a disruption of postingestive feedback (Specific Aim #3) will be assessed with the 24-hr, two-bottle preference test (Experiment l) and a 15-min, single-bottle intake test (Experiment 2). This two-test sequence, involving the same set of rats, should resolve several of the lingering questions that have surrounded the issue of GT- lesion-induced taste deficits for over 30 years. Similarly, the same set of rats will be used in Experiment 3 to reevaluate the influence of GT lesions on the absolute reward value of gustatory stimuli (Specific Aim #2) in a lever pressing task. A different set of rats will participate in Experiments 4 and 5 to examine further the effects of GT lesions on tasks that require the accurate detection of the absolute and relative hedonic value of gustatory stimuli (Specific Aim #2). A third set of rats will be used to address the hypothesis that GT lesions induce a taste learning impairment (Specific Aim #4). The generality of the deficit will be tested by examining performance on aversive (Experiment 6) and appetitive (Experiment 7) taste learning procedures. The short-term goal of the proposed research will be to determine which of these general processes best explains the behavioral deficits that accompany lesions of the taste thalamus. In the long term these experiments may expose general organizing principles applicable to the entire gustatory neuraxis.